feat: do not modify the Content-Type twice when sending strings#6991
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ShubhamOulkar
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Methodology
- Scenario:
res.send('<html>...</html>') - Iterations: 100,000
- Environment: Windows / Node.js
- Metric: Operations per second (ops/sec)
Results
| Metric | Before (Current) | After (Optimized) | Improvement |
|---|---|---|---|
| Total Time | ~501 ms | ~137 ms | ~3.6x Faster |
| Avg Op Time | 0.0050 ms | 0.0014 ms | -72% overhead |
| Throughput | ~200k ops/sec | ~728k ops/sec | +264% |
jonchurch
requested changes
Jan 16, 2026
jonchurch
requested changes
Jan 16, 2026
bjohansebas
commented
Jan 16, 2026
jonchurch
approved these changes
Jan 18, 2026
ShubhamOulkar
suggested changes
Jan 19, 2026
UlisesGascon
approved these changes
Jan 19, 2026
ShubhamOulkar
approved these changes
Jan 19, 2026
…set-twice-content-type
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We were modifying the Content-Type twice when a manual Content-Type was not set (that is, without
res.set('Content-Type', 'text/plain').send('hey')), because it would enter here and then enter here again. This reduces how often we go into thecontent-typelibrary, adds a small performance improvement, and slightly improves CPU usage, building on all the validations thatexpress/lib/utils.js
Line 225 in 2cd372e
For those who do comparisons with a hello-world, this will improve Express’s results, we’re almost catching up to Fastify 😄
The following diffs are based on the simple hello-world example in this repo (https://github.com/expressjs/express/tree/master/examples/hello-world)
diff v4.22.1 vs this pr
diff v4.22.1 vs v5.2.1